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Regex Tester

Test and debug regular expressions with real-time matching, highlighting, and capture group extraction.

Pattern

//g

g(global)

i(case-insensitive)

m(multiline)

s(dotAll)

u(unicode)

Test String

About Regex Tester

Regex Tester is a free online tool for testing and debugging regular expressions. Enter your pattern and test string to see real-time matches with highlighting, capture groups, and match indices. Regular expressions are powerful pattern-matching tools used in programming, text processing, and data validation.

All processing happens entirely in your browser using JavaScript's native RegExp engine. No data is sent to any server, ensuring complete privacy for your test data and patterns.

How to Use

Enter pattern — Type your regular expression in the pattern input field.
Set flags — Toggle flags (g, i, m, s, u) using the checkboxes.
Test — Type or paste your test text. Matches are highlighted in real-time with detailed match information including indices and capture groups.

Supported Regex Flags

g (global) — Find all matches, not just the first one.
i (case-insensitive) — Match letters regardless of case.
m (multiline) — ^ and $ match start/end of each line.
s (dotAll) — Dot (.) matches newline characters.
u (unicode) — Enable full Unicode matching.

Frequently Asked Questions

Q: Is my data secure?

Yes. All processing happens entirely in your browser. No data is ever sent to any server.

Q: Which regex flavor is used?

This tool uses JavaScript's built-in RegExp engine (ECMAScript flavor). Patterns written here will work in JavaScript, TypeScript, and other ECMAScript-compatible environments.

Q: Does it support lookahead and lookbehind?

Yes. JavaScript supports both positive and negative lookahead (?=...) (?!...) as well as lookbehind (?<=...) (?<!...) in modern browsers. These work correctly in this tool.

Q: What are capture groups?

Capture groups are portions of a pattern enclosed in parentheses. They extract specific parts of a match. Named groups (?<name>...) are also supported and displayed in the match details.

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